The present invention relates generally to thread repair inserts and, in particular, to a thread repair insert and method for repairing threaded holes disposed in materials and for repairing threaded holes disposed in materials in which a crack has propagated therethrough such that the repaired threaded hole may receive a threaded fastener via the insert.
Materials often exhibit a variety of different failure mechanisms. On occasion, materials are loaded beyond a tensile strength of the material and the material fractures abruptly and completely. In these circumstances the material is usually non-repairable and must be replaced. However, often materials do not fail in an abrupt complete manner, but rather fail due to fatigue or localized stresses which exceed design criteria, causing cracks to form in the material. Often when these cracks initially form, the material is still functional for its desired purpose. For instance, a reciprocating machine may receive cracks in its structural material and yet continue to operate, albeit at perhaps a lesser efficiency. Cracks thus serve as indicators that a material is being over stressed and yet also provides an opportunity for remedial measures to be taken without requiring entire replacement of the affected material.
Where the crack passes through a preexisting hole, however, such as through a stud hole, or worse, a spark plug hole, a severe problem exists.
Crack repair pins are known in the art which are threaded into holes drilled and tapped in the cracks to prevent cracks from continuing to propagate. U.S. Pat. No. 5,379,505 (issued to the present inventor) provides one example of these crack repair pins. These crack repair pins have been effective in resealing materials such as cast iron casings which require that they maintain a somewhat pressurized environment without allowing fluids to escape therefrom.
In addition, locks are known in the art which can draw cracks together somewhat and extend the life of the material which is cracked. One example of this can be found in the inventor""s U.S. Pat. No. 4,662,806.
However, neither of these solutions nor the prior art which applicant is aware address a threaded hole which needs repair to receive a threaded fastener and specifically, the repair of a threaded hole in which a crack has propagated therethrough. Where the threaded hole is a spark plug hole, the problem is quite severe because of the internal pressures within the combustion chamber.
For example, a damaged threaded hole in which a threaded fastener is to be received in needs to be strengthened to a level which effectively allows the threaded fastener to be rigidly retained therein. In addition, the damaged threaded hole may need to be repaired to a level which allows parts to be coupled to one another to effectively provide a seal which will withstand a pressurized environment. Furthermore, the damaged threaded hole may be disposed in a material at a location which requires the walls of the hole to provide means to maintain a somewhat pressurized environment without allowing fluids to escape therefrom.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant""s acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
The other prior art listed above but not specifically described further catalog the prior art of which the applicant is aware. These references diverge even more starkly from the references specifically distinguished above.
The present invention is distinguished over the known prior art in a multiplicity of ways. For one thing, the present invention provides a thread repair insert which not only repairs threads of a threaded hole but also draws together opposite sides of a crack which may have propagated through the threaded hole. In addition, the thread repair insert according to the present invention provides clamping means which allows the insert to lock into the material to preclude disengagement of the insert from the threaded hole. The clamping means, inter alia, precludes opposite sides of the crack from moving in a direction generally along an axis of the thread repair insert. Furthermore, the thread repair insert strengthens a damaged threaded hole to a level which effectively allows a threaded fastener to be rigidly retained therein and to provide a seal which will withstand a pressurized environment.
In a preferred form, the thread repair insert of the present invention includes a drive head with a means to apply torque thereto, a neck below the head, a shoulder below the neck and a sleeve substantially below the shoulder. Preferably, a thread relief portion is interposed between the shoulder and the sleeve.
The sleeve is provided with an interior thread and an exterior thread. The exterior thread of the sleeve is adapted to be threaded into a hole having a thread pitch which is formed complementally to the exterior thread of the sleeve. The interior threads are preferably adapted to receive a desired standard threaded fastener.
The drive head of the insert can include any of a variety of torque-receiving configurations. For instance, the drive head can have multiple facets dimensioned to be addressed by facets of a wrench. In addition, slots may be formed complementally to a slotted screw driver or other similar structures. Thus, the drive head receives torque and causes the thread repair insert to rotate about a central, long axis thereof.
The neck includes a break-off groove which is interposed between the drive head and the shoulder and preferably defines an area of the thread repair insert having a weakest tensile strength experiencing torsional loads. Thus, when torque is applied through the drive head at greater and greater magnitudes, the thread repair insert fractures at the break-off groove before fracturing in any other location.
The shoulder is interposed between the neck and the exterior threads of the sleeve and includes a cusp exposed at a lower most portion of the shoulder. The cusp is formed by a greater diameter portion and-a lesser diameter portion, with the lesser diameter portion adjacent the exterior threads of the sleeve. Thus, as the thread repair insert is threaded into a complementally formed threaded hole, the cusp of the shoulder abuts against an outer surface of the hole and identifies a point at which the insert can translate no further along the central, long axis. In addition, when the cusp of the shoulder contacts the outer surface of the hole there is a wedging or clamping effect caused by the cusp of the insert and the inter engagement of the threads of the insert within the complementally threaded hole. Therefore, the clamping means precludes disengagement of the insert from the threaded hole and the upheaval of opposite sides of the cracked threaded hole. Furthermore, the thread repair insert strengthens and seals the cracked threaded hole such that a threaded fastener may be received and retained within said threaded hole via the thread repair insert.
The sleeve is a substantially cylindrical construct having a top adjacent the cusp of the shoulder and a bottom defining a surface of the insert opposite the head. The sleeve has threads circumscribing an outer periphery and an inner periphery thereof. The exterior threads disposed on the sleeve include a crest defining a major diameter thereof and a root defining a minor diameter thereof. An upper surface extends from a bottom edge of the root to an upper edge of the crest. A lower surface extends from a top edge of the root to a lower edge of the crest. Specifically, the upper surface extends linearly upward from the bottom edge of the root to the upper edge of the crest. Similarly, the lower edge extends linearly upward from the top edge of the root to the lower edge of the crest. Thus, the upper edge of the crest is closer to the head than the adjacent bottom edge of the root.
In mending the threaded hole, the hole is preferably tapped such that it is configured to have threads substantially complementally to the exterior threads of the thread repair insert. However, a major diameter of the tapped threaded hole may be slightly greater than a major diameter of the thread repair insert. The insert is threaded into the hole by applying torque to the head of the insert causing the insert to rotate and causing the upper surface of the exterior threads to slide along the complementally formed threads of the hole. Thus, drawing opposite sides of the threaded hole toward each other and hence opposite sides of the crack toward each other This torque continues to be applied until the cusp of the shoulder abuts the surface of the material adjacent the threaded hole. At that point, the thread repair insert ceases to be threaded into the material. However, the application of torque continues until a maximum torsional force for the break-off groove of the neck is reached causing the head to shear off at the break-off groove.
In addition, multiple threaded holes may be located along the length of the crack and filled with crack repair stitching pins to further mend the crack. Furthermore, locks may be placed transverse to the crack which fit within complementally formed lock receiving holes to also further mend the crack.
A primary object of the present invention is to provide a new and novel thread repair insert for repairing a threaded hole.
A further object of the present invention is to provide the thread repair insert as characterized above which includes a drive head which is driveable by a commonly available torque-applying instrumentality.
Another further object of the present invention is to provide the thread repair insert as characterized above which further includes a sleeve having interior and exterior threads disposed thereon.
Another further object of the present invention is to provide a thread repair insert as characterized above which includes a shoulder interposed between said drive head and said sleeve.
Another further object of the present invention is to provide the thread repair insert as characterized above wherein the shoulder includes means for opposing central axis translation of the thread repair insert when threaded in a threaded hole.
Another further object of the present invention is to provide a thread repair insert as characterized above wherein the central axis translation opposition means and the exterior threads of the sleeve create opposing forces which preclude the thread repair insert from disengaging from the threaded hole.
Another further object of the present invention is to provide the thread repair insert as characterized above which includes a break-off groove located at a transition area between a top surface of the shoulder and the drive head.
Another further object of the present invention is to provide a thread repair insert as characterized above which is designed to enter a complementally formed hole a finite distance and in which the drive head severs off of the thread repair insert at the break-off groove location prior to the exterior threads of the sleeve becoming damaged.
Another further object of the present invention is to provide a thread repair insert as characterized above which includes means for drawing together opposite sides of a crack which has propagated through a threaded hole.
Another further object of the present invention is to provide a thread repair insert as characterized above which strengthens and seals a cracked threaded hole such that a threaded fastener may be received within said threaded hole via the thread repair insert.
Another further object of the present invention is to provide a thread repair insert as characterized above wherein the exterior threads angle upwards towards the head of the insert.
Another further object of the present invention is to provide a thread repair insert wherein the exterior threads are slightly spaced from each other and maintain a minimum thickness between a root and a crest thereof, providing a durable thread.
Another further object of the present invention is to provide a thread repair insert as characterized above which is simple and inexpensive to manufacture and yet durable in construction.
Another further object of the present invention is to provide a thread repair insert as characterized above for cold crack repair which quickly mends cracks which have propagated within a threaded hole in a material and for receiving a threaded fastener therein.
These and other objects will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures.